FUSED PYRAZOLO, IMIDAZOLO AND TRIAZOLO-TETRAZINES

Tetrazine derivatives of the general formula < IMAGE > [in which R denotes a (C3-8)-cycloalkyl group or a (C1-4)-alkyl, (C2-6)-alkenyl or (C2-6)-alkynyl group, such an alkyl, alkenyl or alkynyl group being unsubstituted or substituted by 1 to 3 substitutents selected from halogen atoms, (C1-4)-alkoxy, -alkylthio, -alkylsulfinyl and -alkylsulfonyl groups and optionally substituted phenyl groups A1 denotes a nitrogen atom or a group -CR =, in which R denotes hydrogen or a substituent R , where R denotes a halogen atom or a (C1-6)-alkyl or -alkenyl group which can carry up to 3 substituents selected from halogen atoms, optionally substituted phenyl groups, and (C1-3)-alkoxy, -alkylthio and -alkylsulfonyl groups, or R denotes a (C3-8)-cycloalkyl group, a cyano, hydroxy, nitro or optionally substituted phenoxy group or a group -COR